1. Field of the Invention
The present invention relates generally to a method of producing metals, and more particularly to a method of producing ferrous metals, especially steels, starting with pre-reduced iron ores.
2. Description of the Prior Art
Various attempts have been made to replace conventional steel-producing methods by reduction of the ore in a blast furnace, the production of pig iron and transformation into steel in the Martin furnace or converter and final refining in the arc furnace. These conventional processes have proved costly in investment and in energy and it has been tried, with varying success, to concentrate into a single continuous sequence of operations the transition from ores to usable metals and alloys.
The initial enrichment of the ores and their reduction are now, by known techniques, posing no particular problems. The difficulties arise at the stage of melting and refining, given the dispersed state of the reduced ore and its large content of residual impurities and oxides which the pre-reduction cannot completely eliminate.
The fusion of these pre-reduced ores in the form of spongy agglomerates in cupola-type vertical furnaces, but heated at their base by gas flames, the molten metal being then treated in the converter, has led to difficulties in regulation and a yield too low to have an advantage over the conventional blast furnace.
It has been tried, with electric blast furnaces, operating without coke, to produce steel directly without the intermediary of pig iron. It does not appear that this technique has had any better success.
Direct fusion in the conventional arc furnace, on the other hand, has the following drawbacks, namely, consumption of expensive electrodes, consumption of oxygen for the refining process, long metallurgical operations lowering the furnace output considerably, electrical power demand varying very rapidly with time and over wide ranges, noise sometimes exceeding the threshold of pain, production of relatively large quantities of dust, discontinuous operation yielding large quantities of metal at rather long intervals, and continual variation in the composition of the bath hardly lending itself to a production by the continuous process.
These drawbacks, especially the operating efficiency, are further aggravated by the local and intense nature of the heating by the arc plasma and the dispersed nature of the pre-reduced ore. For these reasons, this production technique does not appear to deserve further consideration.